Field of the Invention
The present invention relates to a solid-state color imaging apparatus arranged to obtain a color television signal by the use of a solid-state image sensor such as a CCD (Charge Coupled Device) or a MOS type color image sensor.
Various types of solid-state color image sensors each combined with a color filter have hitherto been developed. The output signals of the solid-state color image sensor include luminance information and chrominance information. The former information is obtained by passing the output signal of the solid-state color image sensor through a low-pass filter, and is used as a luminance signal (Y). The latter information, the chrominance is obtained by passing the output signal from the solid-state color image sensor through a band-pass filter. This latter information, i.e., chrominance information, is separated into red information and blue information, by a separating means. This separating means includes a one horizontal line period (hereinafter, referred to simply as 1-H) delay circuit, an adder, and a subtractor. In the adder non-delay chrominance information constituting an output of the band-pass filter and delay chrominance information constituting an output of the 1-H delay circuit are added together, whereby red information is obtained from this adder. On the other hand, in the subtractor, subtraction is performed between the non-delay chrominance information and the delay chrominance information. Blue information is obtained from this subtractor. The red and blue information are subjected to detection by a detector, to become a red signal (R) and a blue signal (B), respectively. The red signal (R), blue signal (B), and luminance signal (Y) are inputted into an encoder, in which a color video signal is composed with the use of these input signals.
In order to obtain a color signal from the output signal of the solid-state color image sensor in the above-mentioned way, it is necessary to perform an operation between the chrominance information of one horizontal line and that of another horizontal line which is adjacent thereto. That is to say, the red signal (R) and the blue signal (B) are obtained using vertical correlation between the two adjacent horizontal lines. Accordingly, a means for performing said operation generates a color alias with respect to that portion of the foreground to be picked up which has no vertical correlation. Namely, a conventional color signal separation circuit carries out its operation based on the assumption that a vertical correlation exists between the colors and brightness of the foreground. When the foreground contains a portion where no vertical correlation exists between its color and that of the background (i.e. when the color and/or brightness of that particular portion of the foreground are in sharp contrast with the color and/or brightness of the background) the video images of the foreground and background contain a color alias at their boundaries.
Further, as mentioned above, the conventional circuit is arranged so that the red information and blue information are subjected to detection by a detector, to become a red signal (R) and a blue signal (B), respectively, which are inputted into the encoder. In the encoder, the red signal (R) and the blue signal (B) are matrixed, whereby a green signal (G) is prepared. In the encoder, thereafter, the red signal (R), blue signal (B), green signal (G), and luminance signal (Y) are composed. According to circumstance, in order to simplify the circuit, the red signal (R), the blue signal (B) and the luminance signal (Y) may be directly used for obtaining the TV iignal without the green signal being made. In such cases, the linearity of the signals are important factors in determining the white tracking, white balance, and hue correction of the picture. However, since the conventional color signal separation circuit is such that the blue information and red information are subjected to AM detection, where a signal having a low brightness level in particular is processed, the white balance deteriorates because the linearity of the detector circuit (diode detector circuit) is bad. That is, it is difficult to obtain a uniform white balance from high to low illumination portions of a subject. Further, for the R, G, B and Y signals, corresponding to signals (which are obtained through filters having good spectrum sensitivity), a color adjustment circuit is provided in many cases. The color adjustment circuit use the R, G, B and Y signals in its calculations. However, the white balance deteriorates because the signal ratio is hhanged by the calculations. Further, if all combinations between R, G, B and Y signals are calculated, the calculation circuit becomes complicated and the adjustment is complex. For this reason, the adjustment can not be achieved in a limited adjusting width.